Is using solar-offset to charge an EV cheating?

Thanks to unusual circumstances — we do not yet have an EV yet, something that, two years ago, I thought we would already have — our 5.59 kW home solar system is producing 200 percent of our home electric use. In fact, it’s been producing 200 percent of our electric use for more than two years!

That’s great for the environment and for helping our neighbors become unknowingly greener 😉 But not so great for us, and perhaps not so great for the environment either, as we continue to drive two old gas clunkers.

Some day – perhaps two years from now – we’ll almost certainly start to draw back some of what will then be close to 20,000 extra kWh our home solar system has produced and which our utility, Xcel Energy, allows us to bank, or keep indefinitely for future use.

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10,000 banked kWhOf course, we’ve only banked our current extra 10,000 kWh mathematically speaking. Practically speaking, all of the extra electricity we’ve produced is gone forever, having been used up immediately by our neighbors.

Economically speaking, there’s no question we should use as many as possible of those 10,000 extra kWh we’ve produced. In fact, at 25 mpg, $3.80 per gallon and 3.5 miles per kWh in an EV, we’re sitting on $5,320 worth of gasoline!

Environmentally speaking, things are a lot cloudier. That’s partly because we’ve created a unique situation – I know of only one other person who’s banked as many solar kWh as we have here in Colorado. In fact, he’s banked MORE!

The lack of clarity surrounding the right thing to do environmentally is also due partly to the unique, and complicated, questions that swirl around the different environmental impacts of EVs and gasoline cars. For example, the whole thorny question of solar offset, which typically involves plugging in a “solar-charged” EV at a time when the actual electricity flowing into its batteries is not being generated 100 percent by solar (it might even be zero percent solar-generated).

I’ve written about these questions before: here, here, and here. And, yes, I know, far less than .001% of people are even aware of such questions, much less concerned about them. But I can’t help myself, I want to know the answers to these questions. That’s why I’d like to track down an expert who could answer the questions below.

What’s better, environmentally speaking: Using a home solar system to (partially) power an electric car that replaces a gasoline car, or using that same home solar system to power one’s current home electric use?

Having recently read a couple of interesting blog entries produced by the Union of Concerned Scientists (UCS) on EVs vs. gasoline cars and their different environmental impact based on different MPG numbers and electric grid numbers, I figured I’d try contacting someone at UCS to see if they might be interested in trying to answer my questions.

I’ll let you know if I get an answer. Since I don’t know if Don will respond , if you know someone who can help me answer these questions definitively, please let me know via comments below this entry 🙂

QUESTION NO. 1. What’s better, environmentally speaking: Using a home solar system to (partially) power an electric car that replaces a gasoline car, or using that same home solar system to power one’s current home electric use?

QUESTION NO. 2: More specific to our own unusual situation: Environmentally speaking, what would be better, for us to –>

a) never pull the extra 10,000 kWh we’ve banked during the last two years for an EV and consider these a donation to our Aurora, Colo. neighborhood while we continue to drive our two gas clunkers(a ’92 Acura Integra & a ’94 Toyota Camry)?

b) pull those extra kWh for two EVs and replace both our gas cars with EVs?

c) consider the banked 10,000 kWh as having been donated to our neighbors and never use those banked kWh, but still buy one new EV, plug it in, and stop sending excess kWh into the grid once we get that electric car, using it to replace one of our two gas cars?

The big-picture question, then, is: What’s better — using home solar to power an EV that will take a gas car off the road, or continuing to drive a gas car and using home solar to power our own current load on the grid plus that of our neighbors?

About The Author

Christof Demont-Heinrich is founder, creator and editor of SolarChargedDriving.Com, which he launched in September 2009. A journalism professor at the University of Denver (DU), Demont-Heinrich is a lifelong environmentalist who loves to bird, hike, camp, and bike. As passionate as he is about the environment -- and about promoting the synergy between solar power and electric cars, he is equally passionate about writing.